I was probably a little ambitious if I said that Canon is the standard. I shoot canon, but many other pro photographers shoot Nikon. Volatile shoots Nikon if i'm not mistaken. I would honestly buy used. I bought one of my markII's used and one new. Places like B&H photo and KEH photo have used sections that are trustworthy. The major differences between a prosumer dslr and the more expensive ones are the iso abilities and the sensor. Most dslr bodies under $2500 used a sensor that isn't full 35mm size. That means that if you use a 28mm lens, that you really only get about 35 degrees out of one of these cameras. A full frame lens makes a huge difference. Also, as time goes on-the ISO capabilities of these cameras just continues to improve. I can shoot at 6400 ISO all day long without any noise...and the newer 1DsMKIV's can go up to something like 15000 iso and stay clean, it's really pretty amazing.
The best piece of advice that I could give anyone starting out is to spend money and buy good glass. I believe that the best lenses for the money in the canon family are the 50 1.4 and the 28 1.8. The 50 1.4 is a legendary portrait lens, and the 28 is super versatile. Learn how to shoot in manual mode while adjusting af points, app, and shutter speed-it will make a world of difference.